Extending scatterometry to the measurements of sub 40 nm features, double patterning structures, and 3D OPC patterns

This paper examines the extendibility of the scatterometry techniques to characterize structures pushing the limits of current lithographic printing technologies. In particular, we investigate the limits of normal-incidence optical CD (NIOCD) measurements using the smallest features afforded by the most recent generation of hyper-NA immersion scanners. Special analysis techniques have also been developed and applied to cases relevant to double exposure and double patterning lithography. Models were used successfully to decouple CD and overlay values associated with patterning the first and second set of features on the wafer, using a single scatterometry measurement. These advances pave the way to the development of full solutions for the general case of double patterning structures with two different populations of lines or structures. In addition, the current study focused on seeking a better understanding of the use of scatterometry 3D features characterization, particularly as it relates to OPC model building and verification. The demonstration of tip-to-tip measurements on 3D structures is very encouraging as it introduces the advantages of scatterometry, such as reduced influence of line-edge roughness (LER) and better precision, to the practice of advanced OPC model building.